Therefore, this left forests and interwoven wetlands as the only viable alternative.

Forests also have very large surface areas and intrinsic mass, and very fortunately turn out to have a many positive attributes for large-scale carbon capture:

1. Forests’ technology is established and thoroughly tested – photosynthesis has been around for about 3.4 billion years.
2. They can operate at truly large scale – forests already absorb about 15.6 billion tons of emitted carbon dioxide every year– over half of all fossil-fuel based emissions.  (Unfortunately, due to deforestation, fires, and other disturbances forests also release 8.1 billion tons of carbon dioxide, leaving the net absorption at 20% of all anthropogenic emissions).
3. The process is highly economic – growing trees is relatively cheap, and when the resulting wood fiber is used in industry, the cost of carbon capture is actually negative.
4. Forest growth also brings many secondary benefits such as biodiversity, environmental improvements, multiuse etc.
5. Silvicultural science on forest growth is relatively well known and established.

Indeed, forests are conceptually the reverse combustion engine: instead of drawing on existing carbon stocks and emitting CO2 into atmosphere, forests absorb atmospheric CO2 and store it in inert, usable, solid cellulose fibers.  

Thus, large scale carbon capture via forests is by far the most attractive prospect. The next analysis to consider therefore is the suitability of each of the three forest biomes: Tropical, Temperate, and Boreal forests.